Strange noises detected in stratosphere using $50 balloons

Novel cheap solar-powered balloons that can be built for $50 apiece have been used to detect some strange noises in the stratosphere.
Christopher McFadden
The balloons are cheap and easy to build.

Darielle Dexheimer, Sandia National Laboratories 

A team of researchers from Sandia National Laboratories has developed simple solar-powered balloons that can be made for less than $50 from common building materials. Made from painter’s plastic, tape, and a dash of charcoal dust, each is 20 feet (6 meters ) to 23 feet (7 meters) tall and can be built on a basketball court.

The balloons require no energy input other than sunlight and can soar to 70,000 feet (21 kilometers) relatively easily. The balloons were developed to carry scientific payloads into the stratosphere.

The stratosphere, a layer of Earth's atmosphere, is known for its peacefulness as it is seldom disturbed by airplanes or turbulence. Despite that, microphones in the stratosphere capture diverse sounds that cannot be heard elsewhere. These sounds comprise natural occurrences such as colliding ocean waves and thunder, human-made sounds such as wind turbines or explosions, and even mysterious sounds with no known source.

To reach the stratosphere, Bowman and his designed and built their simple balloons to reach these heights with the need for more expensive and sophisticated lighter-than-air platforms.

Strange noises detected in stratosphere using $50 balloons
Images of the balloons in use.

“Our balloons are basically giant plastic bags with some charcoal dust on the inside to make them dark. We build them using painter’s plastic from the hardware store, shipping tape, and charcoal powder from pyrotechnic supply stores. When the sun shines on the dark balloons, the air inside heats up and becomes buoyant. This passive solar power is enough to bring the balloons from the surface to over 20 km (66,000 ft) in the sky,” said Bowman. “Each balloon only needs about $50 worth of materials and can be built in a basketball court,” he added.

The researchers gathered data using micro-barometers, primarily designed for monitoring volcanoes, to detect low-frequency sound. GPS tracks the balloons' paths after release, a crucial task as they can travel long distances and land in remote locations. The balloons are cost-effective and straightforward to construct and launch, allowing for gathering a vast amount of data through releasing numerous balloons. In addition to the usual sounds of nature and human activity, Bowman and his team picked up an unidentified sound.

“[In the stratosphere,] there are mysterious infrasound signals that occur a few times per hour on some flights, but the source of these is completely unknown,” said Bowman. In the future, the researchers point out, solar-powered balloons could also help explore other planets, such as observing Venus’ seismic and volcanic activity through its thick atmosphere.

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